THE MIND'S EYE. 



3°9 



side nearest to me, seems directed downward and to the left; again, 

 it has shifted its position and is no longer the front, and the side 

 which appears to be the front seems directed upward and to the right. 

 The presence of the diagonal line makes the change more striking: 

 in one position it runs from the left-hand rear upper corner to the 

 right-hand front lower corner; while in the other it connects the left- 

 hand front upper corner with the right-hand rear lower corner. 



Fig. 15 will probably seem at first glimpse to be the view of a 

 flight of steps which one is about to ascend from right to left. Im- 



Fig. 15a. 



Fig. 155. 



Fig. 15. 



Figs. 15, 15a, and 156. — The two views of Fig. 15 described in the text are brought out more 

 clearly in Figs. 15a and 155. The shaded portion tends to be regarded as the nearer face. 

 Fig. 15a is more apt to suggest the steps seen as we ascend them. Fig. 155 seems to rep- 

 resent the hollowed-out structure underneath the steps. But even with the shading the 



dual interpretation is possible, although less obvious. 



agine it, however, to be a view of the under side of a series of steps; 

 the view representing the structure of overhanging solid masonwork 

 seen from underneath. At first it may be difficult to see it thus, be- 

 cause the view of steps which we are about to mount is a more 

 natural and frequent experience than the other; but by staring at it 

 with the intention of seeing it differently the transition will come, 

 and often quite unexpectedly. 



The blocks in Fig. 16 are subject to a marked fluctuation. Now 



